Technical Question To "Connecting" Blocked By ISP

[ServusTV]

Im clueless what i should tell my ISP, since they're obviously blocking the port or something. Im able to login into my acc on the website but not ingame anymore. It's obviously an ISP issue, i just would like to hear what you would tell your ISP?
Telling them they've blocked a certain Port that i need open again ?

Im playing on warmane for 3 years in a row now and never had any issue when it comes to connecting. Me and my gf played about a week ago and suddenly the next day we both thad the same error. I tried connecting via VPN to see if it's a "warmane" or a "me" issue, when using a VPN i was able to connect so i was curious i literally tried everything.

What i tried:
- redownloading the game
- rechecked realmlist
- restarted pc/router (useless since i have a static IP)
- cleared dns/ip
- reinstalled OS
- disabled firewall / router firewall
- removed folder / files from read only
- changed DNS
- manually portforwarding icecrown/frostmourne/blackrock port (router / pc firewall)
- logging into warmane acc on the website, waiting a bit an then logging in.